The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Compressors are used in a wide variety of industrial and residential applications to circulate refrigerant within refrigeration, Heat, Air Ventilation, and Cooling (HVAC), heat pump, or chiller systems (generally referred to as “refrigeration systems”) to provide a desired heating or cooling effect. In any of these applications, the compressor should provide consistent and efficient operation to ensure that the particular refrigeration system functions properly.
The compressor may include a crankcase to house moving parts of the compressor, such as a crankshaft. In the case of a scroll compressor, the crankshaft drives an orbiting scroll member of a scroll set, which also includes a stationary scroll member. The crankcase may include a lubricant sump, such as an oil reservoir. The lubricant sump can collect lubricant that lubricates the moving parts of the compressor.
When the compressor is off, liquid refrigerant in the refrigeration system generally migrates to the coldest component in the system. For example, in an HVAC system, during an overnight period of a diurnal cycle when the HVAC system is off, the compressor may become the coldest component in the system and liquid refrigerant from throughout the system may migrate to, and collect in, the compressor. In such case, the compressor may gradually fill with liquid refrigerant and become flooded.
One issue with liquid refrigerant flooding the compressor is that the compressor lubricant is generally soluble with the liquid refrigerant. As such, when the compressor is flooded with liquid refrigerant, the lubricant normally present in the lubricant sump can dissolve in the liquid refrigerant, resulting in a liquid mixture of refrigerant and lubricant.
Further, in an HVAC system, upon startup in the morning of a diurnal cycle, the compressor may begin operation in a flooded state. In such case, the compressor may quickly pump out all of the liquid refrigerant, along with all of the dissolved lubricant, in the compressor. For example, the compressor may pump all of the liquid refrigerant and dissolved lubricant out of the compressor in less than ten seconds. At this point, the compressor may continue to operate without lubrication, or with very little lubrication, until the refrigerant and lubricant returns to the suction inlet of the compressor after being pumped through the refrigeration system. For example, it may take up to one minute, depending on the size of the refrigeration system and the flow control device used in the refrigeration system, for the lubricant to return to the compressor. Operation of the compressor without lubrication, however, can damage the internal moving parts of the compressor, result in compressor malfunction, and reduce the reliability and useful life of the compressor. For example, operation of the compressor without lubrication can result in premature wear to the compressor bearings.
Traditionally, crankcase heaters have been used to heat the crankcase of the compressor to prevent or reduce liquid migration to the compressor and a flooded compressor state. Crankcase heaters, however, increase energy costs as electrical energy is consumed to heat the compressor. Additionally, while crankcase heaters can be effective for slow rates of liquid migration, crankcase heaters can be less effective for fast rates of liquid migration, depending on the size or heating capacity of the crankcase heater.